It has been widely known that receptor tyrosine kinases of signal transduction pathway play a role in the development of cancer. Among them, erbB1 and erbB2 belonging to erbB family and expressed in cell membrane are receptor-type proteins having tyrosine kinase activity, and their overexpression in various types of cancers have been reported. ErbB1 is sometimes referred to as EGFR (epidermal growth factor receptor) or HER1, and its overexpression has been identified, for example, in squamous cell carcinoma such as mouth cancer and esophageal cancer, non-small-cell lung cancer, and the like. ErbB2 is sometimes referred to as HER2 or neu, and its over expression has been identified in breast cancer (10-30%), ovarian cancer (about 30%), bladder cancer (30-40%), and the like. As mentioned above, from the fact that the overexpression of erbB1 or erbB2 plays a role in the development of cancer, antibodies against these receptors have been attempted to be used as a molecular-targeted anticancer drug. A specific example includes an anti-erbB2 antibody (common name: Trastuzumab, trade name: Herceptin) for breast cancer and an anti-erbB1 antibody (common name: Gefitinib, trade name: Iressa) for non-small-cell lung cancer. However, administration of the anticancer drug targeting erbB1 or erbB2 is limited to the case of cancer which expresses the above-described receptors in large excess. Therefore, it has been desired to provide a new anticancer drug.
In addition, on the occasion of deciding on courses of treatment of a patient with breast cancer, as mentioned above, presence or absence of overexpression of erbB2 (HER2) has to be determined in advance. The reason is that the patient to be applied with the above-described anti-erbB2 antibody is limited to the case in which the overexpression of erbB2 is identified. For the method for testing the above-described overexpression of erbB2, Hercep Test has been employed conventionally. This is a method of immunostaining of erbB2 expressed on the surface of cell with monoclonal antibody, in which judgment is made by 4 levels of 0, 1+, 2+ and 3+, and the cases of 2+ and 3+ are evaluated as overexpression. As a detection method for this erbB2, it is desirable to detect the activated erbB2 through tyrosine phosphorylation. However, there is a problem that, when specific detection of phosphorylation site is carried out, other phosphorylated erbB family is also detected. Therefore, there remains a problem that it is not clear whether the signaling pathway works actually by the phosphorylation of overexpressed erbB2. Further, even when erbB2 is expressed in large excess, if the signaling of erbB2 does not function practically, the treatment by anti-erbB2 antibody will be inappropriate. Such a problem lies similarly in the detection of erbB1, in the treatment using the anti-erbB1 antibody, and the like.    Non-patent Literature 1: Oncology, vol. 20, p 1763-1771, 2006.    Non-patent Literature 2: Journal of Clinical Oncology, vol. 25, p 587-595, 2007.